The disclosures of Japanese Patent Applications No. 2001-007488 filed on Jan. 16, 2001 and No. 2001-044132 filed on Feb. 20, 2001, each including the specification, drawings and abstract, are incorporated herein by reference in their entirety.
1. Field of Invention
The invention relates to suppression of the discharge of HC from an internal combustion engine of a vehicle to the atmosphere.
2. Description of Related Art
In order to prevent the atmosphere from being polluted by NOx, HC, and CO contained in exhaust gas in an internal combustion engine (hereinafter referred to as engine), present-day vehicles are normally provided with a catalytic converter including a catalyst such as a three-way catalyst having the functions of causing noxious components such as NOx, HC, and CO to react with one another and converting them into harmless components such as N2, CO2, and H2O. Also, an HC adsorbent for temporarily adsorbing and holding a great amount of HC, which is generated especially during cold start of the engine, until the catalyst is warmed up and activated is disposed in an exhaust system upstream of the catalytic converter. The HC adsorbent, which is disposed upstream of the catalytic converter including the three-way catalyst, is either accommodated in a container different from a container for the catalytic converter or accommodated in the container for the catalytic converter while constituting a stratified structure together with the three-way catalyst.
The exhaust system of the engine is provided with the HC adsorbent and the catalytic converter that causes HC, CO, and NOx to react with one another and that converts them into harmless components such as N2, CO2, and H2O. The HC adsorbent temporarily adsorbs and captures a great amount of HC that is generated during cold start of the engine until the catalytic converter is warmed up and activated by exhaust gas in the engine. As soon as the catalytic converter is warmed up and activated, the catalyst thus activated becomes capable of purifying the HC discharged from the HC adsorbent, which is also warmed up by exhaust gas in the engine in the meantime while losing its HC-adsorbing ability. Such a convenient HC-discharge preventing mechanism is obtained in this manner. However, such a combination of the HC adsorbent and the HC oxidation catalyst occasionally leads to the possibility that the HC adsorbent might reach a temperature at which HC is discharged before the HC oxidation catalyst reaches its activation temperature and that HC might be discharged to the atmosphere in between times.
Such a problem constitutes a serious threat especially to an economy-running vehicle equipped with an engine that is stopped temporarily if the vehicle is stopped temporarily because of a red light or traffic jam or to a hybrid vehicle that is suitably driven by either an engine or an electric motor depending on the operational state of the vehicle. This is because of the fact that the engine is often stopped temporarily, that the HC adsorbent and the catalytic converter cool off in the meantime, and that cold start of the engine may be repeated many times.
The invention has been made as a solution to such a problem. It is an object of the invention to reliably suppress the discharge of HC to the atmosphere during cold start of an engine and to thereby improve the properties of exhaust gas in a vehicle whose engine is repeatedly started with great frequency, such as an eco-run vehicle or a hybrid vehicle.
One aspect of the invention provides an HC-discharge suppressing device and an operational method of suppressing the discharge of HC in a vehicle equipped with an engine that has an exhaust system including an HC adsorbent and an HC oxidation catalyst and that is stopped temporarily upon fulfillment of a predetermined condition for operating the vehicle. According to the device and the method, the operation of the engine is controlled after cold start thereof in accordance with a temperature of the HC adsorbent and the HC oxidation catalyst, in such a manner as to minimize the amount of HC discharged from the exhaust system to the atmosphere.
As the HC adsorbent and the HC oxidation catalyst such as a three-way catalyst are heated up, the HC-holding performance of the former and the HC-purifying performance of the latter change as shown in FIG. 1. Referring to FIG. 1, the axis of ordinate represents the HC-holding performance and the HC-purifying performance. The axis of abscissa intrinsically represents temperatures of the HC adsorbent and the HC oxidation catalyst. However, since the HC adsorbent and the HC oxidation catalyst are heated by exhaust gas in the engine and gradually rise in temperature with the lapse of time during cold start of the engine, the temperatures of the HC adsorbent and the HC oxidation catalyst correspond to the elapsed time after cold start of the engine. Thus, if the operation of the engine after cold start thereof is controlled such that the rise of temperatures of the HC adsorbent and the HC oxidation catalyst, which are heated up by exhaust gas in the engine, minimizes the amount of HC discharged to the atmosphere during a period in which exhaust gas in the engine has heated up the HC adsorbent sufficiently but not the HC oxidation catalyst, the area in which a curve indicating the HC-holding performance of the HC adsorbent and a curve indicating the HC-purifying performance of the HC oxidation catalyst overlap with each other is basically increased to a maximum possible extent. This is achieved by controlling the load, air-fuel ratio, ignition timing, and the like such that they best suit the design of each engine, while the engine is being warmed up after cold start thereof. If the discharge of HC during cold start of the engine is thus suppressed to a minimum possible extent, the degree of discharge of HC improves significantly in a vehicle equipped with an engine that is repeatedly stopped temporarily in the course of traveling and that may be restarted at a low temperature after temporary stoppage thereof depending on the degree of warm-up or the period of temporary stoppage, that is, in a vehicle such as an economy-running vehicle or a hybrid vehicle.